Ongoing Algal Blooms Linked To The Largest Die-Off Of Great Whales Ever Recorded

Around 90% of the whales washed ashore have been calves under three months of age. Andrea Chirife/Southern Right Whale Health Monitoring Program

By Josh Davis

28 Oct 2015, 12:18

Along the remote Patagonian coast of Argentina, something isn’t quite right. Baby whales have been washing up on beaches in unprecedented numbers, an event that has been occurring with worrying frequency. What has been responsible for these deaths, which have occurred almost every year for the last decade, has up until now remained elusive, but researchers now think that they have an answer. They have found that the years in which the worst die-offs were experienced also coincided with the highest densities of toxic Pseudo-nitzschia algae.

The unusual number of dead whales washing up started in 2005, with and average of65 recorded dead each year around the calm bays of the remote Valdes Peninsula. Designated a world heritage site, the area is an important calving ground for the southern right whale where the protected water is warmer and calmer than out in the open ocean. Since then, more and more of the cetaceans have been found dead, to the point where the Wildlife Conservation Society declared the situation as the largest die-off of great whales that has ever been recorded.

But it’s not just the number of whales dying that is of concern as, worryingly, 90% of those found are calves under three months old. The carcasses are thought to represent as many as a third of all new born calves born during each season, and with the unusual mortality event occurring almost every year for the past decade, it is making a serious dent on the number of whales in the region.

Toxic algae Pseudo-nitzschia have been linked to a surge in southern right whale deaths in Argentina. NOAA Fisheries/NWFSC

Until now, the cause behind the mass die-off has remained difficult to determine, but researchers from the National Oceanic and Atmospheric Administration now think that they could have an answer. While correlation is not definitive proof, the researchers have found that the number of whale deaths at the peninsula closely follow the concentration of the toxic Pseudo-nitzschia recorded in the ocean. The algae produce the toxin domoic acid, which can accumulate in shellfish and fish and, in turn, poison their predators, such as the whales. The toxin affects the brain of those exposed, causing seizures and death.

“The numbers [of algae and whale deaths] hinge at the same point and have the same pattern,” said Cara Wilson, who led the study, published in the journal Marine Mammal Science, in a statement. “What's unusual about this is how long these bloom events continued to reoccur. You don't usually have deaths every year but the calves died in high numbers every year from 2007 to 2013.”

This is not the first time that algal blooms in the oceans have been linked to the mass die-offs of cetaceans. Over the summer around 30 dead fin whales washed ashore on the Alaskan coast, with algal blooms thought to be reponsible. With the number and frequency of algal blooms expected to increase in the coming years due to a warming of the oceans, the researchers suspect that we are going to only see more and more mass die-offs.

The whales usually use the warm calm waters of the Valdes Peninsula as a calving ground. John Atkinson/Ocean Alliance